scholarly journals Predicting the Heading Misalignment of a Vessel-Shaped Offshore Fish Farm Under Waves and Currents

2018 ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Jungao Wang ◽  
Muk Chen Ong
Keyword(s):  
Reference Site ◽  
Single Point ◽  
Fish Farm ◽  
Misalignment Angle ◽  
Integrated Method ◽  
Open Sea ◽  
Waves And Currents ◽  
Spread Area ◽  
Fish Cages ◽  
Current Reduction

A vessel-shaped fish farm concept for open sea applications has been proposed recently. The whole system consists of a vessel-shaped floater, fish cages positioned longitudinally along the floater, and a single-point mooring system. The whole system weathervanes; this feature increases the spread area for the fish waste. However, the downstream cages may experience reduced water exchange when the vessel is parallel to the currents. This situation may jeopardize the fish health. A dynamic positioning (DP) system may be necessary to improve the flow conditions. This paper investigates the misalignment angle between the heading of the vessel-shaped fish farm and the currents under combined wave and current conditions. The misalignment angle is critical for the estimation of the DP system consumption. A numerical model of the fish farm system with flexible nets is developed. Current reduction factors are included to account for the flow velocity reductions between the net panels. The heading of the system is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. An integrated method using metamodels is proposed and applied for the prediction of the misalignment angle for a reference site. The probability distribution of the misalignment angle between the vessel heading and the currents is calculated using the Kriging metamodel for the reference site. Based on the prediction, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

scholarly journals Numerical Study on the Heading Misalignment and Current Velocity Reduction of a Vessel-Shaped Offshore Fish Farm

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Jungao Wang ◽  
Muk Chen Ong
Keyword(s):  
Numerical Study ◽  
Single Point ◽  
Fish Farm ◽  
Misalignment Angle ◽  
Fish Welfare ◽  
Integrated Method ◽  
Waves And Currents ◽  
Spread Area ◽  
Fish Cages ◽  
Current Reduction

Recently, the concept of a vessel-shaped fish farm was proposed for open sea applications. The fish farm comprises a vessel-shaped floater, five fish cages, and a single-point mooring system. Such a system weathervanes, and this feature increases the spread area of fish waste. Still, the downstream cages may experience decreased exchange of water flow when the vessel heading is aligned with the current direction, and fish welfare may be jeopardized. To ameliorate the flow conditions, a dynamic positioning (DP) system may be required, and its power consumption should relate to the heading misalignment. This paper proposes an integrated method for predicting the heading misalignment between the vessel-shaped fish farm and the currents under combined waves and currents. A numerical model is first established for the fish farm system with flexible nets. Current reduction factors are included to address the reduction in flow velocity between net panels. The vessel heading is obtained by finding the equilibrium condition of the whole system under each combined wave and current condition. Then, the Kriging metamodel is applied to capture the relation between the misalignment angle and environmental variables, and the probability distribution of this misalignment angle is estimated for a reference site. Finally, the requirement for the DP system to improve the flow condition in the fish cages is discussed.

Numerical Analysis of a Vessel-Shaped Offshore Fish Farm

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Andreas Vangdal Høiland ◽  
Muk Chen Ong
Keyword(s):  
Wind Waves ◽  
Single Point ◽  
Fish Farm ◽  
Mooring Line ◽  
Mooring System ◽  
Wave Loads ◽  
Fish Farms ◽  
Mooring Lines ◽  
Environmental Loads ◽  
Fish Cages

The aquaculture industry is aiming to move fish farms from nearshore areas to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves, and currents. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system, and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from the frequency-domain (FD) analysis. A mooring system with six mooring lines was designed to avoid possible interactions with the fish cages. Time-domain (TD) simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared under various wave and current conditions. The effects due to misalignment of wave and current directions on the responses were discussed. Finally, the responses using flexible and rigid net models were compared under steady current conditions.

A Preliminary Study of a Vessel-Shaped Offshore Fish Farm Concept

2017 ◽  
Author(s):  
Lin Li ◽  
Zhiyu Jiang ◽  
Muk Chen Ong
Keyword(s):  
Wind Waves ◽  
Single Point ◽  
Open Water ◽  
Fish Farm ◽  
Mooring Line ◽  
Mooring System ◽  
Wave Loads ◽  
Fish Farms ◽  
Environmental Loads ◽  
Fish Cages

The aquaculture industry is aiming to move fish farms from near-shore area to open seas because of many attractive advantages in the open water. However, one major challenge is to design the structure to withstand the environmental loads due to wind, waves and current. The purpose of this paper is to study a vessel-shaped fish farm concept for open sea applications. The structure includes a vessel-shaped hull, a mooring system and fish cages. The shape of the hull minimizes the wave loads coming from the bow, and the single-point mooring system is connected to the turret at the vessel bow. Such a system allows the whole fish farm to rotate freely about the turret, reduces the environmental loads on the structure and increases the spread area of fish wastes. A basic geometry of the vessel hull was considered and the hydrodynamic properties were obtained from frequency domain analysis. A preliminary mooring system was designed to avoid possible interactions with the fish cages. Time domain simulations were performed by coupling the hull with the mooring system. A simplified rigid model of the fish cages was considered. The global responses of the system and the mooring line loads were compared in various waves and current conditions. The effects due to misalignment of waves and current directions on the responses were also studied.

Proposition of Operational Maps As Tools for Evaluating Safety During the Emergency Disconnection of Risers

2018 ◽  
Author(s):  
Marcelo Anunciação Jaculli ◽  
José Ricardo Pelaquim Mendes ◽  
Kazuo Miura ◽  
Márcio Yamamoto
Keyword(s):  
Material Properties ◽  
Drilling Fluid ◽  
Environmental Loads ◽  
Finite Elements Modeling ◽  
Sea Bottom ◽  
Open Sea ◽  
Operational Safety ◽  
Waves And Currents ◽  
Drilling Operations ◽  
Water Depths

The construction of subsea wells under deep water depths brought the necessity to understand the behavior of columns on such conditions. These columns can be risers, drill strings or casing strings, which are either being installed by lowering them until they reach the sea bottom and/or inside the well, or they are already connected and fully operational. Since these columns are exposed to the open sea, environmental loads such as waves and currents will affect them. Depending on how harsh these environmental conditions are, drilling operations may be suspended. Therefore, understanding how such loads interact with such columns are of the utmost importance if one wants to ensure operational safety. In this paper, we discuss about the problem of emergency disconnections of risers. The concern of doing an emergency disconnection is fundamental for ensuring operational safety because the well will lose a safety barrier, as the level of the drilling fluid inside the well can no longer be controlled after the riser is disconnected, and thus the fluid cannot maintain its downhole pressure anymore. This work focuses on a finite elements modeling of riser dynamics, with the appropriate applied loads, to verify under which sea conditions the riser must be disconnected. The result of such analysis is called an “operational map”, which displays the maximum values of stress along the riser as a function of different sea conditions. Using the riser material properties, this map can then be divided in two regions — failure and admissible — and thus one can see for which sea conditions the riser must be disconnected to avoid its failure. The contribution of the present study is proposing a methodology to elaborate an operational map for a given riser scenario, from which both failure and admissible regions can be seen for emergency disconnection operations.

Numerical Analysis of a Floating Fish Cage With Feeding Systems

2020 ◽  
Author(s):  
Lin Li ◽  
Mathias Bruset ◽  
Muk Chen Ong ◽  
Xiaopeng Wu
Keyword(s):  
Environmental Conditions ◽  
Numerical Study ◽  
Coupled System ◽  
Feeding Tube ◽  
Fish Farm ◽  
Dynamic Responses ◽  
Feeding System ◽  
Solidity Ratio ◽  
Sensitivity Studies ◽  
Fish Cages

Abstract A modern marine-based fish farm normally consists of a feeding barge, several fish cages, and feeding tubes. Although many studies, both experimental and numerical, are available in the literature to investigate the global responses of the fish cages under wave and current conditions, research on the coupled system including both the fish cage and the feeding system is very limited. This paper presents a numerical study on the coupled system with a floating fish cage and the feeding system. The purpose is to study the dynamic responses of the coupled system under different environmental conditions and configurations of the fish farm. A numerical model is firstly established in the numerical program OrcaFlex, comprising of a feeding barge, a gravity-based floating fish cage with mooring systems, and a feeding tube between the barge and the cage. Time-domain simulations of this coupled system are then performed under environmental conditions corresponding to 1-year and 50-year return periods for a reference site. The deformation of the fish cage, the tensions in the anchor lines and in the feeding tube are compared under various conditions. Sensitivity studies on the solidity ratio of the fish net as well as the lengths of the feeding tube are addressed, and their influences on the responses of the coupled system are also discussed.

scholarly journals A Field Survey of Waves and Currents in Seabathing Area facing Open Sea

1997 ◽  
Vol 13 ◽  
pp. 741-746
Author(s):  
Shigeo Takahashi ◽  
Kojiro Suzuki ◽  
Tomomitsu Okamura ◽  
Hironobu Miura ◽  
Syunji Sakamoto ◽  
...  
Keyword(s):  
Field Survey ◽  
Open Sea ◽  
Waves And Currents

Hydrodynamic performance of a semi-submersible offshore fish farm with a single point mooring system in pure waves and current

2020 ◽  
Vol 90 ◽  
pp. 102075 ◽  
Author(s):  
Xiao-Hua Huang ◽  
Hai-Yang Liu ◽  
Yu Hu ◽  
Tai-Ping Yuan ◽  
Qi-You Tao ◽  
...  
Keyword(s):  
Single Point ◽  
Fish Farm ◽  
Hydrodynamic Performance ◽  
Mooring System

Environmental Description in the Design of Fish Farms at Exposed Locations

2017 ◽  
Author(s):  
David Kristiansen ◽  
Vegard Aksnes ◽  
Biao Su ◽  
Pål Lader ◽  
Hans V. Bjelland
Keyword(s):  
Marine Fish ◽  
Environmental Conditions ◽  
Measurement Data ◽  
Field Measurements ◽  
Fish Farm ◽  
Fish Farms ◽  
Coastal Regions ◽  
Waves And Currents ◽  
Farm Structures

This paper addresses the description of exposure from waves and currents in coastal regions for design of marine fish farms. Representative descriptions of environmental conditions are important inputs to the design and dimensioning of reliable fish farm structures. A trend with moving production to more exposed sites and introduction of new and novel fish farm structures increase the need for more precise descriptions of the marine environment to keep control of uncertainties in design. Dedicated field measurements at two exposed aquaculture sites from February to December 2016 are presented. Results from statistical analyses of the measurement data demonstrate that common practice for characterization of exposure in design of fish farms has several deficiencies that should be improved to reduce uncertainties in design.

Numerical Investigation on the Cage-to-Cage Wake Effect: A Case Study of a 4 × 2 Cage Array

2021 ◽  
Vol 143 (5) ◽  
Author(s):  
Jaesub Sim ◽  
Hui Cheng ◽  
Karl Gunnar Aarsæther ◽  
Lin Li ◽  
Muk Chen Ong
Keyword(s):  
Drag Force ◽  
Fish Farm ◽  
Fish Farms ◽  
Wake Effect ◽  
Cage System ◽  
Flow Interactions ◽  
Wake Effects ◽  
Fish Cages ◽  
Cage Fish

Abstract Aquaculture has been the world’s fastest-growing food producing method and grown to become the second-largest export industry in Norway during the past 40 years. Usually, the high-value fish such as Atlantic Salmon (Salmo Salar) is raised in a multi-cage fish farm, where the flow interactions between fish cages exist. In this study, the interactions between fish cages are implemented into the numerical program, FhSim, to investigate its influences on the responses of a multi-cage fish farm. Tensions in anchor lines, drag force, and cultivation volume of each cage in a full-scale 4 × 2 multi-cage fish farms under different flow directions are analyzed numerically. The discrepancies of the responses based on three cases, i.e., (i) without any wake effects, (ii) with only cage-to-cage wake effect, and (iii) with all the wake effects, are compared and discussed. The results indicate that neglecting the wake effects will overestimate the total drag force of the eight cages up to 128% and underestimate the total cultivation volume of the eight cages as much as 42%. This study can provide suggestions on how to consider the wake effects during the design of the multiple-cage system.

Effects of waves and currents on gravity-type cages in the open sea

2008 ◽  
Vol 38 (2) ◽  
pp. 105-116 ◽  
Author(s):  
Chai-Cheng Huang ◽  
Hung-Jie Tang ◽  
Jin-Yuan Liu
Keyword(s):  
Open Sea ◽  
Waves And Currents
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